Chemically amplified resist compositions

ABSTRACT

Provided is a chemically amplified resist composition comprising a photoacid generator which releases, by exposure to light, an acid containing both a sulfonic acid group and a carboxyl group; and an acid sensitive resin which contains a dissolution controlling group to be cleaved therefrom by the action of the acid, thereby forming a carboxy-containing alkali soluble resin; or a chemically amplified resist composition comprising a photoacid generator and an acid sensitive resin which has a huge molecular weight and from which the dissolution controlling group is cleaved owing to the decomposition of the partially crosslinked structure by the acid released from the photoacid generator. By the above-described composition, ultrafine processing can be carried out with improved focal depth, whereby an excellent rectangular pattern can be formed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a chemically amplified resistcomposition and more specifically, to a chemically amplified resistcomposition improved in the depth of focus.

[0003] 2. Description of the Prior Art

[0004] In the fields of the fabrication of various devices typified by asemiconductor device, which require fine processing on the order ofsubmicrons, there is an increasing demand for actualizing higherdensification and higher integration. Under such situations, therequirements for photolithography have become severer.

[0005] In recent days, a chemically amplified resist attracts attentionsin such fields. This chemically amplified resist makes use of thecatalytic action of an acid formed by exposure to light. It ischaracterized in that since the generation efficiency of an acid is higheven under the conditions providing only small exposure energy, it hashigh sensitivity and high resolution.

[0006] The resist is composed principally of a photoacid generator whichreleases an acid and an acid sensitive resin which undergoes a markedchange in the solubility in an aqueous alkaline solution, which is adeveloper, owing to the generation of the acid.

[0007] As an example of the prior art, a chemically amplified resistcomposition comprising, as an photoacid generator,N-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide and, as an acidsensitive resin, a (hydroxystyrene)-(tert-butylcarboxystyrene) copolymercan be mentioned.

[0008] When the above-described resist is exposed to light, first-stagereaction occurs in accordance with the below-described reaction scheme(6), whereby N-(p-toluenesulfonyloxy) -5-norbornene-2,3-dicarboxyimideused as a photoacid generator is decomposed and p-toluenesulfonic acid(p-toluenesulfonic acid ion) which is an acid component, is released.

[0009] Then, in the second-stage reaction, the acid thus released actson the acid sensitive resin, that is, a(hydroxystyrene)-(tert-butylcarboxystyrene) copolymer, whereby the acidsensitive resin is converted-into an alkali-soluble(hydroxystyrene)-(tert-carboxystyrene) copolymer in accordance with thebelow-described reaction scheme (7). This alkali-soluble resin isdissolved in an alkali developer, whereby development is effected.

[0010] The alkali development is allowed to proceed through the reactionprocedures as described above. Owing to a high generation efficiency ofan acid in exposed regions, a pattern of high resolution is available.

[0011] Owing to the recent tendency to higher densification and higherintegration, it has come to be impossible to sufficiently satisfy therequest for ultra-fine processing of a device even by using such aresist.

[0012] For example, when the above-described resist was applied to asilicon substrate, followed by exposure to light and development by aKrF stepper under the optical conditions of NA of 0.60 and σ of 0.75 toform a contact hole pattern of 0.20 μm, the depth of focus thus obtainedwas only 0.60 μm. It was therefore difficult to form a contact holehaving a sufficient rectangularity.

[0013] On the surface of a wafer, there exists unevenness due to innercircuits. When a resist is applied onto such unevenness, this unevennessis reproduced to some extent on the surface of the resist. In this case,best focus is not always available all over the wafer. The depth offocus, which is a focus margin, must be sufficiently deep for ultra-fineprocessing even in such a case.

[0014] In FIG. 2, an inner circuit 22, an intrastratum insulating film23 and a resist layer 24 are formed over a substrate 21. This drawingillustrates how the resist layer 24 is exposed to light for theformation of a contact hole in the intrastratum insulating film 23, onthe supposition that a substrate wafer is exposed to light at threeplaces by moving the stage having the substrate wafer placed thereon.

[0015] The resist layer 24 reproduces, on its surface, unevenness of theinner circuits. In this case, a distance between the light source forexposure and the resist layer is not always constant on the wholesurface of the wafer. Moreover, the light intensity upon exposure has apredetermined distribution. For example, in spite of the best focus atthe site (2), the sites (1) and (3) are under the state of defocus andthe intensity of the light incident on the resist inevitably becomesweak. When a conventional resist is employed, exposure is insufficientat the site of weak light intensity, leading to a marked reduction inresolution.

[0016] A description was so far made of the lowering in the resolutiondue to shortage in the light intensity upon exposure. In addition, afilm decrease upon alkali development becomes one factor for disturbingultrafine processing.

[0017]FIG. 3 is a schematic view illustrating the etching of theintrastratum insulating film 32 with a resist pattern formed over theintrastratum insulating film 32 laid over the substrate 31. In FIGS.3(b-1) to 3(b-3), an ordinarily employed resist 33 b is used. As isapparent from FIG. 3(b-2), a developer causes a film decrease of theresist 33 b, which prevents the formation of a good rectangular pattern.When the intrastratum insulating film is etched using this pattern, thenarrowing of the intrastratum insulating film occurs. This pattern istherefore not suited for ultrafine processing.

SUMMARY OF THE INVENTION

[0018] An object of the present invention is therefore to provide achemically amplified resist composition which permits ultrafineprocessing improved in the depth of focus and is excellent in thepattern rectangularity, in consideration of the above-describedproblems.

[0019] In a first aspect of the present invention, there is thusprovided a chemically amplified resist composition comprising anphotoacid generator which releases an acid by exposure to light and anacid sensitive resin which has an alkali soluble group protected with adissolution controlling group and is converted into an alkali solubleresin by the cleavage of the dissolution controlling group caused by theaction of the acid, wherein the acid contains a sulfonic acid group anda carboxyl group and the alkali soluble resin contains a carboxyl group.

[0020] In the above-described chemically amplified resist composition,the photoacid generator is preferably a compound represented by thefollowing formula (1):

R¹(CO)₂N—OSO₂—R²—COOC(CH₃)₃   (1)

[0021] wherein R¹ represents a dicarboxyimide compound residue and R²represents a cyclohexylene or phenylene group.

[0022] In the above-described chemically amplified resist composition,the acid sensitive resin is preferably represented by thebelow-described formula (2) or (3) and has a weight-average molecularweight of 3,000 to 30,000:

[0023] wherein R³ represents a tert-butyl group, tetrahydropyranyl groupor R⁴(R⁵O)CH— in which R⁴ and R⁵ each independently represents a C₁₋₄alkyl group, x stands for 0.4 to 0.9 and y stands for 0.1 to 0.9.

[0024] In the above-described chemically amplified resist composition,the photoacid generator is incorporated in an amount of 1 to 15 wt. %relative to the acid sensitive resin.

[0025] In a second aspect of the present invention, there is alsoprovided a chemically amplified resist composition comprising anphotoacid generator which releases an acid by exposure to light, and anacid sensitive resin which has an alkali soluble group protected with adissolution controlling group and is converted into an alkali solubleresin by the cleavage of the dissolution controlling group caused by theaction of the acid, wherein the acid sensitive resin is represented bythe below-described formula (4) or (5) and has a weight-averagemolecular weight of 100,000 to 5,000,000:

[0026] wherein R⁶ represents a crosslinked structure of —O—C(CH₃)₂—O— or—CO—O—C(CH₃)₂—O—CO—, R⁸ represents a hydroxyl group or a carboxyl group,z stands for 0.1 to 0.9 and w stands for 0.1 to 0.9.

[0027] In the chemically amplified resist composition, when thecrosslinked structure R⁶ of the acid sensitive resin is—CO—O—C(CH₃)₂—O—CO—, the photoacid generator is preferably a compoundrepresented by the following formula (1):

R¹(CO)₂N—OSO₂—R²—COOC(CH₃)₃  (1)

[0028] wherein R¹ represents a dicarboxyimide compound residue and R²represents a cyclohexylene or phenylene group.

[0029] In the chemically amplified resist composition, the photoacidgenerator is incorporated in an amount of 1 to 15 wt. % relative to theacid sensitive resin.

[0030] The chemically amplified resist composition according to thefirst aspect of the present invention comprising a photoacid generatorwhich releases, by exposure to light, an acid containing both a sulfonicacid group and a carboxyl group; and an acid sensitive resin whichundergoes cleavage of a dissolution controlling group by the action ofthe acid to form an alkali soluble resin containing a carboxyl group hasa remarkably improved maximum dissolution rate and also improved focusdepth by the association of the sulfonic-acid-containing acid with thealkali soluble resin in an alkali developer.

[0031] The chemically amplified resist composition according to thesecond aspect of the present invention comprises a photoacid generatorand an acid sensitive resin which has a huge molecular weight and fromwhich the dissolution controlling group is cleaved by the decompositionof the partial crosslinked structure due to the acid released from thephotoacid generator. This chemically amplified resist has a sufficientmolecular weight at unexposed regions, which makes it possible to lowerthe minimum dissolution rate and to form a good rectangular pattern,thereby improving the depth of focus.

[0032] Moreover, by using, in combination, the photoacid generator whichreleases an acid containing both a sulfonic acid group and a carboxylgroup by exposure to light, and an acid sensitive resin which forms acarboxyl-containing alkali soluble resin by the decomposition of itspartial crosslinked structure caused by the acid, it is possible tosimultaneously accomplish an increase of the maximum dissolution rateand decrease of the minimum dissolution rate, whereby the excellentfocal depth is available.

[0033] Use of such a chemically amplified resist composition having adeep focal depth makes it possible to conduct ultrafine processing suchas formation of a contact hole of 0.20 μm or less or formation of acircuit having a line spacing or line width of 0.15 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a log-log graph illustrating the relationship betweenthe exposure energy of a resist and dissolution rate;

[0035]FIG. 2 illustrates how the resist having unevenness on its surfaceis exposed to light, wherein indicated at numeral 21 is a substrate, 22an inner circuit, 23 an intrastratum insulating film and 24 a resistlayer;

[0036]FIG. 3 is a schematic view for describing the rectangularity bycomparing resist patterns formed using resists different in the maximumdissolution rate, wherein indicated at numeral 31 is a substrate, 32 anintrastratum insulating film, 33 a a resist layer having a small minimumdissolution rate and 33 b a resist layer (conventional resist) having anordinary minimum dissolution rate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0037] The present inventors paid particular attentions to thesolubility of a resist in an alkali. FIG. 1 is a log-log graphillustrating the relationship between the exposure energy of the resistand dissolution rate. As illustrated in this drawing, at smallerexposure energy, the dissolution rate is low and shows the minimum fixedvalue (minimum dissolution rate), indicating difficulty in developmentat the site where exposure is blocked by a mask or the like. Thedissolution rate starts a drastic increase at the exposure energyincreased to a certain value. By a further increase in the exposureenergy, the dissolution rate shows the maximum fixed value (maximumdissolution rate). This maximum dissolution rate indicates easiness ofdevelopment at the mask opening site.

[0038] When the exposure properties of a resist as shown in FIG. 1 aretaken into consideration, there are two methods to attain an improvementin the focal depth, which is an object of the present invention. Thefirst one is to raise the maximum dissolution rate while substantiallymaintaining the minimum dissolution rate.

[0039] Described specifically, an improvement in the maximum dissolutionrate enables a sufficient dissolution rate even at a site where theintensity of light is low, which makes it possible to attain sufficientresolution at a defocus site, such as the site (1) or (3) in FIG. 2,where the intensity of an incident light on the resist is weak.

[0040] The second method is to lower the minimum dissolution rate whilesubstantially maintaining the maximum dissolution rate. Describedspecifically, in this method, a film decrease in an alkali developer issuppressed by controlling the solubility of the unexposed site of theresist in an alkali developer.

[0041] FIGS. 3(a-1) to (a-3) are schematic views illustrating how theintrastratum insulating film 32 is etched when the resist 33 a having asmall minimum dissolution rate is employed.

[0042] Since the minimum dissolution rate of the resist is suppressed toa lower level, a film decrease does not occur easily at an unexposedportion of a resist pattern as shown in FIG. 3(a-1), which is differentfrom that shown in FIG. 3(b-1). Thus, a good rectangular pattern withexcellent focal density is formed. Favorable patterning free fromnarrowing can be conducted by etching of the intrastratum insulatingfilm through the resulting pattern.

[0043] As described above, an improvement in the focal depth of aresist, which is an object of the present invention, can be attained andsufficient resolution is available even in ultra fine processing, byraising the maximum dissolution rate of the resist, lowering its minimumdissolution rate, or adopting both measures. The maximum dissolutionrate or minimum dissolution rate to be raised or lowered variesdepending on the kind of a light source employed.

[0044] First, a description will next be made of the composition of aresist for attaining the first method. A chemically amplified resistcomposition is formed of, as essential ingredients, a photoacidgenerator which releases an acid by exposure to light and an acidsensitive resin which is converted to an alkali soluble resin by theacid thus released.

[0045] The photoacid generator employed in the first method of thepresent invention must release an acid containing therein both asulfonic acid group and a carboxyl group when exposed to light. Anyphotoacid generator can be used in the present invention insofar as itsatisfies the above-described condition and releases an acid withsufficiently high efficiency by exposure to light.

[0046] Examples of such a compound include compounds each represented bythe following formula (1):

R¹(CO)₂N—OSO₂—R²—COOC(CH₃)₃  (1)

[0047] wherein R¹ represents a dicarboxyimide compound residue and R²represents a cyclohexylene or phenylene group.

[0048] Specific examples includeN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide,N-(p-tert-butylcarboxybenzenesulfonyloxy)-phthalimide,N-(p-tert-butylcarboxybenzenesulfonyloxy)-naphthalimide,N-(p-tert-butylcarboxycyclohe xylsulfonyloxy)-5-norbornene-2,3-dicarboxyimide,N-(p-tert-butylcarboxycyclohexylsulfonyloxy)-phthalimide andN-(p-tert-butylcarboxycyclohexylsulfonyloxy)-naphthalimide. The chemicalformulas of the above-exemplified compounds are shown in Table 1. TABLE1 Chemical formula Name

N-(p-tert- butylcarboxybenzene- sulfonyloxy)-5-norbornene-2,3-dicarboxyimide

N-(p-tert-butylcarboxy- benzenesulfonyloxy)- phthalimide

N-(p-tert-butylcarboxy- benzenesulfonyloxy)- naphthalimide

N-(p-tert-butylcarboxy- cyclohexylsulfonyloxy)-5- norbornene-2,3-dicarboxyimide

N-(p-tert-butylcarboxy- cyclohexylsulfonyloxy)- phthalimide

N-(p-tert-butylcarboxy- cyclohexylsulfonyloxy)- naphthalimide

[0049] As the acid sensitive resin, usable is a resin which contains analkali soluble group protected with a dissolution controlling group andis converted into a carboxyl-containing alkali soluble resin by cleavageof the dissolution controlling group owing to the action of the acidreleased from the photoacid generator.

[0050] Examples of such an acid sensitive resin include resins eachhaving a weight-average molecular weight of 3,000 to 30,000 andrepresented by the below-described formula (2) or (3):

[0051] wherein, R³ represents a tert-butyl group, a tetrahydropyranylgroup or R⁴(R⁵O)CH— in which R⁴ and R⁵ each independently represents aC₁₋₄ alkyl group, x stands for 0.4 to 0.9, preferably 0.5 to 0.75, morepreferably 0.55 to 0.65 and y stands for 0.1 to 0.9.

[0052] Use of such a photoacid generator and an acid sensitive resin incombination brings about a marked improvement in the maximum dissolutionrate of an exposed portion in an alkali developer, because the carboxylgroup of the acid released from the photoacid generator associates, inan alkali developer, with the carboxyl group of the alkali soluble resinformed by the cleavage of the dissolution controlling group from theacid sensitive resin. As a result, the alkali soluble resin acquires asulfonic acid group, thereby having notably improved affinity with thealkali developer.

[0053] For example, whenN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideand (hydroxystyrene)_(m)-(p-tert-butylcarboxystyrene)_(n) correspondingto a KrF light source are used as a photoacid generator and an acidsensitive resin, respectively, the photoacid generator is converted, byexposure to light, into p-tert-carboxybenzenesulfonic acid(p-tert-carboxybenzenesulfonic acid ion) in accordance with the reactionscheme (8).

[0054] The resulting acid causes a reaction to remove the dissolutioncontrolling group (tert-butyl group) from the acid sensitive resin inaccordance with the reaction scheme (7), whereby an alkali soluble resin(hydroxystyrene)_(m)- (p-carboxystyrene)_(n) is formed.

[0055] Since this (hydroxystyrene)_(m)-(p-carboxystyrene)_(n) contains acarboxyl group, it smoothly associates withp-tert-carboxybenzenesulfonic acid in an alkali developer as shown inthe formula (9).

[0056] As a result, owing to the action of a sulfonic acid group, theaffinity of the alkali soluble resin with the alkali developer shows aremarkable improvement, leading to a rise in its maximum dissolutionrate.

[0057] Also in the case where (carboxytetracyclododecylmethacrylate)_(m)-(tert-butylcarboxytetracyclododecyl methacrylate)_(n)is used, for example, as the resin corresponding to an ArF light source,it associates with p-tert-carboxybenzenesulfonic acid in an alkalideveloper as shown in the reaction scheme (10), which heightens themaximum dissolution rate.

[0058] A description will next be made of the composition of the resistfor attaining the second method of the present invention. Similar to theresist used in the first method, the chemically amplified resistcomposition in this second method comprises, as essential ingredients, aphotoacid generator which releases an acid by exposure to light and anacid sensitive resin which is converted into an alkali soluble resin bythe acid thus released.

[0059] In this method, the acid sensitive resin has, in the moleculethereof, a partial crosslinked structure for lowering the minimumdissolution rate.

[0060] More specifically, the acid sensitive resin has a weight-averagemolecular weight of 100,000 to 5,000,000 and is represented by thebelow-described formula (4) or (5):

[0061] wherein, R⁶ represents —O—C(CH₃)₂—O— or —CO-O—C(CH₃)₂—O—CO—, R⁸represents a hydroxyl or carboxyl group, z stands for 0.1 to 0.9 and wstands for 0.1 to 0.9. This resin will hereinafter be calledcrosslink-structured resin.

[0062] Next, the reaction mechanism upon exposure will be describedusing, as an example, an acid sensitive resin which is a resincorresponding to a Krf light source and has a hydroxystyrene skeletonand has, as a crosslinked structure, an isopropylideneoxy group(—O—C(CH₃)₂—O—).

[0063] The isopropylidene group, which is a dissolution controllinggroup, is cleaved by the acid as shown in the reaction scheme (11),whereby the acid sensitive resin is converted into an alkali solubleresin.

[0064] When a resin having a carboxytetracyclododecyl methacrylateskeleton is used as a resin corresponding to an ArF light source, analkali soluble resin is formed, as shown in the reaction scheme (12), bythe reaction mechanism similar to that shown in the reaction scheme(11).

[0065] In either case, the acid sensitive resin having a weight-averagemolecular weight of 100,000 to 5,000,000 is sparingly soluble in analkali developer at an unexposed portion, which makes it possible tosufficiently lower the minimum dissolution rate. On the other hand, thecrosslinked portion forming a giant molecule is cleaved by exposure tolight, which largely lowers the molecular weight during the process toform an alkali soluble resin, while maintaining the maximum dissolutionrate at a similar level to that of the conventional resist composition.When the crosslinked structure R⁶ represents —CO—O—C(CH₃)₂—O—CO— in theformula (4) or (5) of the acid sensitive resin, it is preferred to usethe photoacid generator of the first method and releases an acidcontaining both a sulfonic acid group and a carboxyl group by exposureto light, because when the crosslinked structure CO—O—C(CH₃)₂—O—CO— iscleaved by the action of an acid as shown in the reaction scheme (13),the alkali soluble resin thus formed contains a carboxyl group.

[0066] Such a resist composition is effective both for lowering theminimum dissolution rate and raising the maximum dissolution rate.

[0067] In the chemically amplified resist composition according to thepresent invention, the photoacid generator is incorporated in an amountof 1 to 15 wt. %, preferably 5 to 10 wt. % relative to the acidsensitive resin.

[0068] In the chemically amplified resist composition according to thepresent invention, a solvent is used in order to dissolve therein thephotoacid generator and acid sensitive resin. As preferred solvents,PGMEA (propylene glycol monomethyl ether acetate) and EL (ethyl lactate)can be used. For example, PGMEA is used singly for a resin correspondingto a KrF light source, while a 1:1 mixed solvent of PGMEA and EL is usedfor a resin corresponding to an ArF light source.

[0069] The acid sensitive resin is preferably incorporated in an amountof about 11 to 21 wt. % based on the whole resist solution and thesolvent is preferably added in an amount of about 79 to 89 wt. % basedon the whole resist solution.

[0070] It is possible to add, to the chemically amplified resist of thepresent invention, known additives such as tackifier, leveling agent andanti-foaming agent within an extent not damaging the characteristics ofthe present invention.

[0071] As a preferred example of the alkali developer usable for thechemically amplified resist composition of the present invention, anaqueous solution containing TMAH (tetramethoxyammonium hydroxide)represented by the formula (14) can be mentioned. For example, a 2.38%TMAH aqueous solution can be used for the development of a resincorresponding to an KrF light source, while a 0.12% TMAH aqueoussolution can be used for the development of a resin corresponding to anArF light source.

EXAMPLES Example 1

[0072] As an acid sensitive resin, a resin represented by the formula(2) wherein R³ represents a tert-butyl group and x stands for 0.57 andhaving a weight-average molecular weight of 15,000 was employed.

[0073] A resist composition comprising 16 wt. % of the acid sensitiveresin, 1.6 wt. % (10 wt. % of the acid sensitive resin) ofN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideas a photoacid generator and 82.4 wt. % of PGMEA as a solvent wasapplied to a silicon substrate to form a film having a thickness of 0.70μm. The resulting film was then exposed to light by a KrF stepper underthe optical conditions of NA of 0.60 and σ of 0.75, whereby a contacthole pattern of 0.20 μm was formed. As an alkali developer, a 2.38% TMAHaqueous solution was employed.

[0074] Based on the cross-sectional observation of the pattern formedafter development, the depth of focus was evaluated.

[0075] Upon alkali development, the maximum dissolution rate and theminimum dissolution rate were evaluated at varied exposure energies byusing a resist dissolution rate measuring apparatus manufactured byPerkin-Elmer Corporation.

[0076] As a result, it was found that the composition had excellentfocal depth of 1.00 μm, a maximum dissolution rate as high as 1.0 μm/s,and a minimum dissolution rate of 10⁻⁵ μm/s which was substantially thesame as that of the ordinarily-employed resist composition correspondingto an KrF light source.

Comparative Example 1

[0077] A resist composition comprising 16 wt. % of the acid sensitiveresin employed in Example 1, 1.6 wt. % (10 wt. % of the acid sensitiveresin) of N-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide as aphotoacid generator and 82.4 wt. % of PGMEA as a solvent was applied toa silicon substrate to form a film having a thickness of 0.70 μm. Theresulting film was then exposed to light by a KrF stepper under theoptical conditions of NA of 0.60 and σ of 0.75, whereby a contact holepattern of 0.20 μm was formed. As an alkali developer, a 2.38% TMAHaqueous solution was employed.

[0078] As a result of the evaluation under the utterly same conditionsas those in Example 1, the composition was found to have a focal depthas shallow as 0.60 μm, a maximum dissolution rate of 0.3 μm/s, and aminimum dissolution rate of 10⁻⁵ μm/s.

Example 2

[0079] As an acid sensitive resin, employed was a crosslink-structuredresin represented by the formula (4) wherein R⁶ represents —O—C(CH₃)₂—O—and z stands for 0.5 and having a weight-average molecular weight of3,000,000.

[0080] A resist composition comprising 17 wt. % of the acid sensitiveresin, 1.7 wt. % (10 wt. % of the acid sensitive resin) ofN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideas a photoacid generator and 81.3 wt. % of PGMEA as a solvent wasapplied to a silicon substrate to form a film having a thickness of 0.50μm. The resulting film was then exposed to light by a KrF stepper underthe optical conditions of NA of 0.60 and a of 0.75, whereby a stripepattern having a line spacing and line width, each 0.18 μm was formed.As an alkali developer, a 2.38% TMAH aqueous solution was employed.

[0081] As a result of the evaluation under the utterly same conditionsas those of Example 1, it was found that the composition had excellentfocal depth of 0.80 μm and a maximum dissolution rate as high as 1.0μm/s. It was also found that the composition had a minimum dissolutionrate of 10⁻⁶ μm/s, which was smaller than that of theordinarily-employed resist corresponding to a KrF light source. Therectangularity of the pattern was excellent.

Comparative Example 2

[0082] In a similar manner to Example 2, film formation, patternformation and evaluation were carried out using the resist compositionemployed in Comparative Example 1.

[0083] As a result, the composition was found to have a focal depth asshallow as 0.50 μm, a maximum dissolution rate of 0.3 μm/s, and aminimum dissolution rate of 10⁻⁵ μm/s.

[0084] In addition, the cross-sectional observation revealed theoccurrence of a film decrease.

Example 3

[0085] As an acid sensitive resin, a resin represented by the formula(3) wherein R³ represents a tert-butyl group and y stands for 0.60 andhaving a weight-average molecular weight of 12,000 was employed.

[0086] A resist composition comprising 17 wt. % of the acid sensitiveresin, 0.85 wt. % (5 wt. % of the acid sensitive resin) ofN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideas a photoacid generator and 82.15 wt. % of a 1:1 mixed solvent of PGMEAand EL as a solvent was applied to a silicon substrate to form a filmhaving a thickness of 0.70 μm. The resulting film was then exposed tolight by an ArF stepper under the optical conditions of NA of 0.60 and aof 0.75, whereby a contact hole pattern of 0.2 μm was formed. As analkali developer, a 0.12% TMAH aqueous solution was employed.

[0087] As a result of the evaluation under the utterly same conditionsas those of Example 1, it was found that the composition had excellentfocal depth of 0.60 μm and a maximum dissolution rate as high as 0.08μm/s. These values are much superior to those of the ordinarily employedresist corresponding to an ArF light source. It was also found that aminimum dissolution rate was 10⁻³ μm/s, which was almost equal to thatof the ordinarily-employed resist corresponding to an ArF light source.

Comparative Example 3

[0088] A resist composition comprising 15 wt. % of the acid sensitiveresin employed in Example 3, 0.75 wt. % (5 wt. % of the acid sensitiveresin) of N-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide as aphotoacid generator and 84.25 wt. % of a 1:1 mixed solvent of PGMEA andEL as a solvent was applied to a silicon substrate to form a film havinga thickness of 0.70 μm. The resulting film was then exposed to light byan ArF stepper under the optical conditions of NA of 0.60 and σ of 0.75,whereby a contact hole pattern of 0.20 μm was formed. As an alkalideveloper, a 0.12% TMAH aqueous solution was employed.

[0089] As a result of the evaluation under the utterly same conditionsas those in Example 1, the composition was found to have a focal depthas shallow as 0.30 μm, a maximum dissolution rate of 0.02 μm/s, and aminimum dissolution rate of 10⁻³ m/s.

Example 4

[0090] As an acid sensitive resin, employed was a crosslink-structuredresin represented by the formula (5) wherein the cross-linked structureR⁶ represents —CO—O—C(CH₃)₂—O—CO— and w stands for 0.4 and having aweight-average molecular weight of 4,000,000.

[0091] A resist composition comprising 16 wt. % of the acid sensitiveresin, 0.8 wt. % (5 wt. % of the acid sensitive resin) ofN-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide as a photoacidgenerator and 83.2 wt. % of a 1:1 mixed solvent of PGMEA and EL as asolvent was applied to a silicon substrate to form a film having athickness of 0.50 μm. The resulting film was then exposed to light by aKrF stepper under the optical conditions of NA of 0.60 and σ of 0.75,whereby a stripe pattern having a line spacing and line width, each 0.15μm, was formed. As an alkali developer, a 0.12% TMAH aqueous solutionwas employed.

[0092] As a result of the evaluation under the utterly same conditionsas those of Example 1, it was found that the composition had excellentfocal depth of 1.00 μm, a maximum dissolution rate of 0.02 μm/s, whichwas equal to that of the ordinarily employed resist corresponding to anArF light source, and a minimum dissolution rate of 10⁻⁴ μm/s, which wassmaller than that of the ordinarily-employed resist corresponding to anArF light source. In addition, the rectangularity of the pattern wasexcellent.

Comparative Example 4

[0093] In a similar manner to Example 4, film formation, patternformation and evaluation were carried out using the resist compositionemployed in Comparative Example 3.

[0094] As a result, the composition was found to have a focal depth asshallow as 0.50 μm, a maximum dissolution rate of 0.02 μm/s, and aminimum dissolution rate of 10⁻³ μm/s.

[0095] In addition, the cross-sectional observation revealed theoccurrence of a film decrease.

Example 5

[0096] A resist composition comprising 17 wt. % of the acid sensitiveresin employed in Example 4, 0.85 wt. % (5 wt. % of the acid sensitiveresin) ofN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideas a photoacid generator and 82.15 wt. % of a 1:1 mixed solvent of PGMEAand EL as a solvent was applied to a silicon substrate to form a filmhaving a thickness of 0.50 μm. The resulting film was then exposed tolight by a KrF stepper under the optical conditions of NA of 0.60 and σof 0.75, whereby a stripe pattern having a line spacing and line width,each 0.15 μm, was formed. As an alkali developer, a 0.12% TMAH aqueoussolution was employed.

[0097] As a result of the evaluation under the utterly same conditionsas those of Example 1, it was found that the composition had excellentfocal depth of 1.10 μm, a maximum dissolution rate of 0.08 μm/s, whichwas equal to that of the ordinarily employed resist corresponding to anArF light source, and a minimum dissolution rate of 10⁻⁴ μm/s, which wassmaller than that of the ordinarily-employed resist corresponding to anArF light source. In addition, the rectangularity of the pattern wasexcellent.

[0098] It should be noted that in the present invention, theweight-average molecular weight is a value as measured by liquidchromatography (in terms of styrene).

What is claimed is:
 1. A chemically amplified resist compositioncomprising an photoacid generator which releases an acid by exposure tolight and an acid sensitive resin which has an alkali soluble groupprotected with a dissolution controlling group and is converted into analkali soluble resin by the cleavage of the dissolution controllinggroup by the action of the acid, wherein said acid contains a sulfonicacid group and a carboxyl group and said alkali soluble resin contains acarboxyl group.
 2. A chemically amplified resist composition accordingto claim 1, wherein the photoacid generator is a compound represented bythe following formula (1): R¹(CO)₂N—OSO—R²—COOC(CH₃)₃  (1) wherein R¹represents a dicarboxyimide compound residue and R² represents acyclohexylene or phenylene group.
 3. A chemically amplified resistcomposition according to claim 1, wherein the acid sensitive resin has aweight-average molecular weight of 3,000 to 30,000 and is represented bythe following formula (2) or (3):

wherein R³ represents a tert-butyl group, tetrahydropyranyl group orR⁴(R⁵O)CH— in which R⁴ and R⁵ each independently represents a C₁₄ alkylgroup, x stands for 0.4 to 0.9 and y stands for 0.1 to 0.9.
 4. Achemically amplified resist composition according to claim 2, whereinthe acid sensitive resin has a weight-average molecular weight of 3,000to 30,000

and is represented by the following formula (2) or (3): wherein R³represents a tert-butyl group, tetrahydropyranyl group or R⁴(R⁵O)CH— inwhich R⁴ and R⁵ each independently represents a C₁₋₄ alkyl group, xstands for 0.4 to 0.9 and y stands for 0.1 to 0.9.
 5. A chemicallyamplified resist composition according to claim 1, wherein the photoacidgenerator is incorporated in an amount of 1 to 15 wt. % relative to theacid sensitive resin.
 6. A chemically amplified resist compositionaccording to claim 2, wherein the photoacid generator is incorporated inan amount of 1 to 15 wt. % relative to the acid sensitive resin.
 7. Achemically amplified resist composition according to claim 3, whereinthe photoacid generator is incorporated in an amount of 1 to 15 wt. %relative to the acid sensitive resin.
 8. A chemically amplified resistcomposition according to claim 4, wherein the photoacid generator isincorporated in an amount of 1 to 15 wt. % relative to the acidsensitive resin.
 9. A chemically amplified resist composition comprisingan photoacid generator which releases an acid by exposure to light, andan acid sensitive resin which has an alkali soluble group protected witha dissolution controlling group and is converted into an alkali solubleresin by the cleavage of the dissolution controlling group by the actionof the acid, wherein said acid sensitive resin has weight-averagemolecular weight of 100,000 to 5,000,000 and represented by thefollowing formula (4) or (5):

wherein R⁶ represents a crosslinked structure of —O—C(CH₃)₂—O— or—CO—O—C(cH₃)₂—O—CO—, R⁸ represents a hydroxyl group or a carboxyl group,z stands for 0.1 to 0.9 and w stands for 0.1 to 0.9.
 10. A chemicallyamplified resist composition according to claim 9, wherein when thecrosslinked structure R⁶ is —CO—O—C(CH₃)₂—O—CO—, the photoacid generatoris a compound represented by the following formula (1):R¹(CO)₂N—OSO₂—R²—COOC (CH₃)₃  (1) wherein R¹ represents a dicarboxyimidecompound residue and R² represents a cyclohexylene or phenylene group.11. A chemically amplified resist composition according to claim 9,wherein the photoacid generator is incorporated in an amount of 1 to 15wt. % relative to the acid sensitive resin.
 12. A chemically amplifiedresist composition according to claim 10, wherein the photoacidgenerator is incorporated in an amount of 1 to 15 wt. % relative to theacid sensitive resin.